The range of applications of probe systems for measuring physical or chemical, measured variables of a medium, e.g. of a fluid, especially a liquid, in process technology is numerous. For example, the manufacture of sterile solutions in pharmaceutical or food processes requires the use of measuring probes for monitoring the product, or the process. The measuring probes can be pH measuring probes, conductivity measuring probes, optical or electrochemical measuring probes for determining a concentration of a substance contained in the medium to be monitored, e.g. a substance such as O2, CO2, certain ion types, organic compounds.
From the state of the art, it is known to perform an inline-measuring of fluids, e.g. products of chemical processes, in the case of which probe systems with axially movable immersion tubes, in which a measuring probe is held, are used. Such probe systems are also referred to as “retractable assemblies”. These retractable assemblies are secured on a process container, for example, a pipe conveying the fluid to be monitored by measuring, and include a treatment chamber, into which the measuring probe can be moved by means of the immersion tube temporarily during operation for calibration- or washing, and/or rinsing, purposes and therein brought in contact with a calibration liquid and/or with a washing, and/or rinsing, medium for cleaning. When the calibration-, or washing, and/or rinsing, procedure is finished, the measuring probe can, thereafter, be moved back into the fluid to be monitored, in order to continue with the inline measuring. In such case, contamination of the monitored fluid with calibration liquid, or, conversely, a contamination of the calibration liquid with fluid being monitored is counteracted with the assistance of seals, which seal the treatment chamber and the process container relative to one another.
For retractable assemblies for use in sterile processes, it has been suggested to provide a second treatment chamber. Thus, for example, in DE 38 20 405 C2, a retractable assembly is described, which has a housing with a housing nozzle connectable to a reaction vessel, wherein, in the housing, there is an immersion tube with a measured value sensing probe, whose measuring head is surrounded by a cage with passageways. The immersion tube can be viewed axially from a measuring position out of the housing nozzle into a retracted rest position in the housing, and back again into the measuring position. In the rest position, the opening of the housing nozzle is sealed by means of a closure. In the rest position, the front part of the immersion tube with the measuring head of the probe facing the reaction vessel is located in a first washing and/or rinsing chamber of the housing, which has an inlet and a drain. Associated with the rinsing chamber in the housing is a second rinsing chamber, further remote from the reaction vessel and having its own inlet and its own drain. In the rest position, a washing and/or rinsing and/or sterilizing of the measuring probe and of parts of the immersion tube can be performed by sending wash-, rinse-, or sterilization medium through the first and the second rinsing chambers. In this way also, those parts of the immersion tube and/or the probe can be cleaned and sterilized, which, in the case of the out viewing of the probe into the measuring position come into the first rinsing chamber. Therewith, it should be prevented, that not washed, or rinsed, and sterilized parts of the immersion tube and the probe come into the rinsing chamber, in which, in given cases, medium of the reactor vessel is contained, and cause contamination.
The drain of the second rinsing chamber is connected with the inlet of the first rinsing chamber via a liquid transport line, so that wash-, rinse- or sterilization medium introduced into the second rinsing chamber goes further via the liquid transport line and the inlet of the first washing and/or rinsing chamber into the first washing and/or rinsing chamber and from there via the drain of the first rinsing chamber is fed to a condensate drain or to a wash, or rinse, drain. This construction does, however, not permit supplying only a single rinsing chamber with liquid.
Between the first and second rinsing chamber in the case of the retractable assembly described in DE 38 20 405 C2, a seal is arranged, which seals the two washing, and/or rinsing, chambers relative to one another. In the region of this seal, no sufficient cleaning, or sterilization of the immersion tube is assured. Especially, also the seal itself cannot be sufficiently cleaned or sterilized.
Also in German patent application DE 10 2005 051 279 A1, a retractable assembly for use in sterile processes is described. Such an assembling includes a housing, which has a space for accommodating a measuring probe and a first chamber for accommodating a first fluid, e.g. a calibration fluid or a washing, and/or rinsing, fluid. The first chamber is in communication with the space for accommodating the probe. The housing includes furthermore a connecting section, by means of which the housing is connectable, or in connection, with a container, which serves for accommodating a medium, whose property is to be measured with the probe. In the housing, there is at least a second chamber for accommodating a second fluid, which should be uncritical both relative to the first fluid as well as also relative to the medium. An example of a second fluid is sterile water. The second chamber is arranged between the first chamber and the connecting section of the housing. In the case of defective seals, so should the probability for a contamination of the medium by the first fluid as well as also a contamination of the first fluid by the medium be lessened.
The probe is accommodated in an immersion tube, in which openings are provided for access of the medium, or a rinsing liquid, to the measuring head. The probe can be moved axially within the housing between a measuring position, in which the probe with its measuring head surrounding a sensor protrudes inwardly into the medium and a washing, and/or rinsing, position, in which the measuring head is arranged within the first rinsing chamber. In order also in the washing, and/or rinsing, position to assure a sealing of the second rinsing chamber arranged between the first rinsing chamber and the medium relative to the medium, the distance between the front end of the probe and the openings in the region of the measuring head of the probe must be greater than the axial length of the second rinsing chamber, i.e. than the distance between the two seals, which seal the second rinsing chamber from medium, on the one hand, and from the first rinsing chamber, on the other hand. As a result, this brings about that, for a certain immersion depth of the measuring head in the medium in measurement operation, a stroke of the immersion tube must be produced, which is enlarged by the axial length of the second rinsing chamber. Additionally, the front end of the immersion tube reaching beyond the position of the actual measuring head by, thus, this length requires correspondingly much space, so that the retractable assembly can only be applied to process containers having a certain minimum volume.
An object of the invention is to provide a probe system of the initially described type, which permits a calibrating of the measuring probe and/or a sufficient sterilizing of the immersion tube and the measuring probe in the state secured on the process container.